The field of the present invention is antifriction bearings of the ball type having an annular inner and outer raceway containing the balls along with an annular separator member. More particularly, the invention relates to ball bearings for very high speed applications wherein only marginal, as opposed to flooded, lubricating and cooling fluid flow is provided to the bearing.
Ball bearings having steel races and steel balls and being capable of sustaining both radial and axial (thrust) loads under conditions of high speed operation are known. These bearings must be provided with adequate flow of lubricating and cooling liquid. This lubricating flow is provided by flooding the bearing with oil, or by providing a marginally lubricating oil mist carried in an air stream.
Also known are ball bearings for use at indeterminate speeds having steel inner and outer races and nonmetallic balls. These bearings may employ ball elements of gem stone or mineral. Such a teaching is set forth in U.S. Pat. No. 1,332,176, issued Feb. 24, 1920 to K. Heindlhofer. Alternatively, these bearings may employ ball elements of ceramic or glass material. A ball bearing teaching the use of ceramic ball elements for decidely low speed operation is set forth in U.S. Pat. No. 2,158,156, issued May 16, 1939 to H. Schroder. Bearings having steel races and steel or ceramic ball elements have been employed for moderately high speed operation with oil flood or marginal oil mist lubrication in an air flow.
However, in selected aerospace turbine engine applications it is desirable to employ the jet fuel of the engine as lubricant and coolant in the engine bearings. Unfortunately, when compared with oil, jet fuel is not a good lubricant. Ball bearings of known construction have been employed with steel balls flooded or marginally lubricated by JP-4 jet fuel with moderate success up to a DN number of about 5.times.10.sup.5. Those skilled in the bearing art will recognize the DN number as being the product of bearing inner race bore diameter in millimeters and rotational speed during use in rotations per minute (RPM). However, when operated with other fuels, such as JP-5, these same bearings have failed under the same operating conditions. JP-4 fuel is recognized as containing trace elements such as sulphur and nitrogen compounds which are not present to the same extent in JP-5 fuel, and which are thought to act as lubricants.
Accordingly, conventional thinking in the bearing art has held heretofore that a ball bearing having steel inner and outer races and steel or ceramic ball elements could not be operated at DN numbers above 5.times.10.sup.5 when lubricated by jet fuel. The demands of advancing technology in the aerospace turbine engine field call for ball thrust bearings capable of operating at DN numbers above 5.times.10.sup.5, and desirably for very high speed operation in the DN number range of 1.times.10.sup.6 to 2.times.10.sup.6, or higher. This operating speed range is, of course, well beyond the known operating limits for lubrication of a ball bearing with jet fuel.